What does quantum theory have to say about how sound propagates?

[__Ben__]

What we hear as sound is a pressure wave moving through the air, sound is the energy from an action being propagated through the atmosphere. That works basically the same in any medium.

 

So, is there any kind of science that tries to explain this macro effect of sound, via quantum theory?

 

[swansont]

I'm not sure why it would be necessary for the cases where classical theory does a good job, like sound in air, but there is a quantum theory: Phonons. Used mostly where you have lattices.

 

https://en.wikipedia.org/wiki/Phonon

http://nanoscale.blogspot.com/2009/02/what-is-phonon.html

[__Ben__]

Well I know they're trying to unify the theories, I just thought maybe quantum mechanics could describe sound better.

 

"The equations in this section either do not use axioms of quantum mechanics or use relations for which there exists a direct correspondence in classical mechanics"

[Delta1212]

Well I know they're trying to unify the theories, I just thought maybe quantum mechanics could describe sound better.

 

"The equations in this section either do not use axioms of quantum mechanics or use relations for which there exists a direct correspondence in classical mechanics"

What need unifying are quantum mechanics and general relativity. They describe different phenomena from one another, and do so with incredible accuracy, but don't seem to be compatible with each other.

 

Classical mechanics is really just "how things work in the most frequently observed and easily tested occurances by humans." It's a set of special cases of the other two and generally provides very accurate descriptions of most things you'd care to understand in your day to day activities but wildly inaccurate descriptions of anything at the extremes of size, speed, energy, distance, etc. Classical mechanics doesn't really need to be unified with anything.

 

It's like a book on tomatoes and dogs to quantum mechanics' encyclopedia of plant life and relativity's encyclopedia of animals. If you want to know about tomatoes, you could go through the time and effort of researching them in the giant compendium of all plant life, but it'd be faster to just look in the book about tomatoes and dogs and you'd get approximately equivalent information. If you want to know about any other plant, that book isn't going to be nearly as helpful.

[Enthalpy]

Phonons have their usefulness in crystals to define curves of E versus p and deduce how they interact with electrons or change the interaction of photons and electrons. As well, some phonons in crystals have a huge frequency, making individual ones more interesting.

 

In air, where sound speed is essentially constant, frequency is low and electrons not so interesting, why use quantum mechanics and define phonons? The classical description has the fabulous advantage of being understandable and useable - QM less so...